Pressurized dispensing apparatus

ABSTRACT

Apparatus for dispensing material under propellant pressure, particularly highly viscous material, includes a container having a piston therein, the material to be dispensed being located on one side of the piston and the propellant on the other. Penetration of propellant into the material to be dispensed is prevented by providing sealant which engages the container wall and slides with the piston, the sealant being of flowable material such as organic and mineral liquids and greases and mastics based on these or aqueous based gels and mastics.

This invention relates to a container adapted to dispense its contentsunder pressure. Particularly, but not exclusively, the invention isconcerned with the dispensing of viscous materials from a containerunder pressure of a propellant.

A vast range of materials are routinely dispensed from pressurisedcontainers of the commonly named "aerosol" type. In such containers thematerial to be dispensed ("the product") lies within the containereither in admixture with or in solution in the propellant. Thistechnology, therefore, is suitable only for dispensing products which donot interact with or deteriorate in the presence of the propellant.Also, such containers normally dispense the product as a fine mist butthey can be adapted to dispense the product as an unbroken liquidstream.

A small number of special container designs are known for dispensingproducts which have to be held out of contact with the propellant. Thereare, generally speaking, two types of these containers, the "collapsiblebag" type and the "piston" type. In the collapsible bag arrangement theproduct is held in a flexible bag secured to the neck of the containerwith an outlet valve extending outwards for exit of the product; thepropellant is held between the bag and the container wall. Underpressure the bag collapses and extrudes the product from the exit valve.Problems with this arrangement are that the bags are permeable to thepropellant causing bubbles to form in the product, and also the bagstend to collapse in an unpredictable manner and incompletely, whichleaves amounts of the product trapped therein and unusable.

In the "piston" type the container is divided into two chambers by aninternal piston, product is held on one side of the piston andpropellant on the other. Under pressure of the propellant the pistonforces the product from the container.

We have carried out much investigation over several years into theoperation of the piston type of dispenser and the operational problemsthereof. They are not common in the market-place; those which areavailable appear to satisfy their specific uses but one major problemprevents their unrestricted general application to products of any kind.That major problem is penetration of the propellant into the product. Ifthe presence of the propellant deteriorates the product, and manymaterials are affected adversely then the known packs cannot be used.Even if the product is chemically inert to the propellant, thepropellant may nevertheless from gas bubbles in the product and break upthe extruded stream of product.

The present invention provides a piston type of dispenser which can beused for dispensing any material but its development was undertaken todispense semi-solid mastics, adhesives and silicone sealants most ofwhich are extremely sensitive to contact with the propellant.

Many mastics, sealants and adhesives are available commercially is smallpackages in squeeze-tube packs and in larger quantities in cylindricaltubes, one end of which is formed by a slidable piston. In use, amanually operable "skeleton gun" is supplied which clamps around thetube and by exerting pressure by a screw twist or by a trigger actuatedpump action the piston is forced manually through the tubular container.The main difficulties with this arrangement are the cost of the gun andthe difficulty of maintaining a constant manual pressure in order toextrude a stream of product of uniform dimensions while at the same timeguiding the stream of product along a line of application.

British patent application No. 2015655 to Schumacker describes adispenser for liquids and pastes in which there is provided a containerhaving therein a piston, which is propelled by gaseous propellant,having first and second wall-engaging skirt portions and therebetween anumber of wall-engaging scraper rings. Held between two adjacent scraperrings is an elastic or flexible ring made of foam. It is thought thatsuch an arrangement would not provide a barrier of sufficientimpenetrability to passage of propellant into the product to bedispensed.

An object of the present invention is to obviate or mitigate theaforesaid problems.

According to the present invention there is provided a dispenser fordispensing a product under pressure of a propellant including acontainer, a piston slidable in the container and dividing same into aproduct chamber for product to be dispensed and a propellant chamber, aflowable sealant material engaging the container wall and slidable withthe piston, closure means for retaining propellant within the propellantchamber and a product outlet extending from the product chambercharacterised in that the flowable sealant material comprises a liquidsubstance providing a substantially impenetrable barrier to thepropellant.

Preferably the piston is a composite piston including a firstwall-engaging surface and a second wall-engaging surface thewall-engaging flowable sealant material being located between saidsurfaces.

Preferably the composite piston comprises a primary piston having awall-engaging skirt, a secondary piston having a wall-engaging skirt andbetween said pistons deformable sealant material whereby under pressurethe deformable material is pressed between the pistons and urged againstthe container wall to form a seal.

Preferably also the primary piston is in frictional engagement with thewall and the secondary piston is in loose fit, thus to encouragepressing of the interposed deformable sealant material.

It is further preferred that the dispenser additionally includes amembranous partition wall within the propellant chamber and formingtherein a propellant compartment.

The sealant material may be any liquid which is chemically compatiblewith the materials it will come into contact with in use. Water itselfand water-based materials such as aqueous gel of alginic materials orgelatin are suitable, as are many organic and mineral oils, greases andwaxes. Liquids such as ethylene glycol, diethylene glycol and glycerolare suitable for many applications. Many resinous and polymericsubstances such as polyvinyl alcohol, silicones and acrylic resins canbe used. Indeed, in general, any liquid can be used, subject only totheir compatibility with the materials it will be in contact with, suchas the propellant. Water and water-based gels are suitable forhalocarbon propellants. To facilitate handling of the liquid sealantduring manufacture and to assist in maintaining contact between sealantand piston so that they travel together, the liquid may be absorbed onto a solid filler material to form a flowable dough-like mass, formedinto a gel or absorbed on a body of foamed plastics material.

The use of a liquid sealant is advantageous in that dents and otherimperfections and the seams of seamed containers will be filled andsmoothed out by the sealant as the pistons pass.

The invention will now be described, by way of example, with referenceto the accompanying drawings of which

FIG. 1 is a part-sectional perspective view of a dispenser of thisinvention;

FIG. 2 is an exploded view of the pistons and membrane shown in FIG. 1;

FIG. 3 is a cross-section through the parts shown in FIG. 2 and

FIG. 4 is a cross-section of one alternative composite piston.

Referring to FIGS. 1 and 2, a dispenser consists of an elongatecylindrical container 1 (which may be an extruded or a seamed can)having a top 2 and inturned domed base 3, the top having a neck 4 andfitted therein a valved outlet extrusion valve 5.

The precise details of the valve are not relevant to the inventiondescribed herein. It is sufficient for the purposes of the presentinvention that the design and dimensions of the valve and nozzle be suchthat will permit the product to be dispensed to exit via the valve. Thedesign of the valve will be selected in accordance with, mainly, theviscosity of the product.

Within the container 1 there are, located serially from top to bottom, aprimary piston 6, a secondary piston 7 and a membranous partition 8.Located between pistons 6 and 7 there is a mass of liquid sealantmaterial 9. These parts divide the internal volume of the container intoa chamber 10 for product to be dispensed and a chamber 11 forpropellant. The presence of the membrane 8 is optional but, whenpresent, it forms with the base 3 a propellant compartment 12. The base3 has a generally central hole for introduction of propellant duringfilling after which it is closed by a plug 13. The crown of the primarypiston 6 is shaped to conform generally to the internal configuration ofthe can top and internal parts of the valve 5 so as to maximise theamount of product which can be expelled by the piston.

Referring to FIG. 3, the primary piston 6 has a slightly domed crown 20and a wall-engaging skirt 21. There is formed in the piston 6 a domedrecess 22, the purpose of which will be described later. Secondarypiston 7 has a wall-engaging skirt 30 and a high-domed piston crown 31.Membrane 8 is a thin-walled film of nylon, domed in shape, with anoutwardly-directed flange 40. The container base 3 is also of domedconfiguration and has central filling port 50 which is plugged byresilient plug 13.

It should be noted that when base 3 is crimped to the container theflange of the membrane 8 is folded into the crimped joint. The curvatureof the dome of the base 3 and the membrane 8 are different so as to formtherebetween a product compartment (12 in FIG. 1). The curvature of themembrane 8 and the dome of the secondary piston 7 are substantially thesame. A body of deformable sealant is located between the pistons 6 and7.

FIG. 4 illustrates one possible alternative form of composite piston.This is a single piston having a first wall-engaging surface 60, asecond wall-engaging surface 61 with an annular recess 62 locatedbetween the surfaces 60 and 61 which is filled with the body ofdeformable sealant material.

The deformable sealant material 9 is preferably of a soft kneadableconsistency or even a viscous liquid or a grease.

A brief description of the preferred method of filling and assembly ofthe dispenser will now be given.

Product is charged into the empty unturned container 1 which may beprior purged with inert gas. A primary piston 6 is then force fitted onthe end of a ram, into the container 1. To facilitate insertion of thepiston 6, the ram carries a dome-ended probe which is dimensioned toengage the domed recess 22 in the piston 6. The application of pressureon the centre of the piston causes the piston to flex permitting air orinert gas to escape past the piston leaving the product chamber free ofgas. A body of the sealant 9 is then injected into the skirt of thepiston 6, followed by insertion of the secondary piston 7 in a similarmanner as for the primary piston 6 to which pressure is applied to forcethe sealant outwards against the container wall to form a seal. Aflexible membrane 8 of domed shape with an out-turned annular lip islaid across the open end of the container and then the domed base 3 iscrimped on to the container. The curvature of the base 3 and themembrane 8 are different so as to form a compartment 12 therebetween.Propellant is injected into the compartment 12 via its central aperturewhich is then closed by a plug 13. The curvature of the membrane 8conforms to the curvature of the crown of the secondary piston 7 and is,at least initially, supported thereby.

The pack has a prolonged shelf life. Since the propellant is effectivelyencapsulated in the sealed compartment 12, the only possible manner inwhich the propellant can escape to deteriorate the product would be bymolecular diffusion through the membrane itself. Even if diffusionoccurred, or if the membrane was faulty and ruptured, any propellantpresent in chamber 11 would be contained therein by the double pistonsand the sealant.

In use, the valve 5 is opened releasing the internal pressure, thepropellant in chamber 12 expands thereby stretching the membrane 8 andforcing secondary piston 7 into even closer contact with the sealant 9which is urged outward against the container wall. Primary piston 6advances and extrudes the product from the valve. During continued usethe membrane 8 eventually ruptures releasing propellant into chamber 11.Thus, the main purpose of membrane 8 is to prolong shelf life and thepurpose of the sealant 9 is to prevent contact of propellant and productduring use.

As the pistons 6 and 7 move along the container wall it is possible forsealant to be lost by passage into the product or propellant chambers ifthere is extensive damage in the form of longitudinal creases or dentsin the container thus depleting the reservoir of sealant held betweenthe pistons. If a large enough amount of the sealant is lost in this waythe domed crown 31 of the secondary piston 7 comes into contact with thedomed recess 22 of the primary piston 6 and the piston pair continue tomove forward in physical engagement.

It is convenient to dimension the secondary piston 7 such that thecapacity within its skirt and dome represent the ullage of thecontainer.

It is preferred that the primary piston and the valve assembly be madeof high density polyethylene such as RIGIDEX (Trade Mark) or of nylonthe secondary piston of low density polyethylene and the membrane ofthin film nylon.

I claim:
 1. A dispenser for dispensing a product under pressure of apropellant, including a container, a piston slidable in the containerand dividing same into a product chamber for product to be dispensed anda propellant chamber, a flowable sealant material engaging the containerwall and slidable with the piston, closure means for retainingpropellant within the propellant chamber and a product outlet extendingfrom the product chamber characterised in that the flowable sealantmaterial comprises a liquid substance providing a substantiallyimpenetrable barrier to the propellant, the piston being a compositepiston including a first wall-engaging surface and a secondwall-engaging surface, the wall-engaging flowable sealant material beinglocated between said surfaces, in which the composite piston comprises aprimary piston having a wall-engaging skirt, a separate independentlyslidable secondary piston having a wall-engaging skirt and between saidprimary and said secondary pistons a (deformable) flowable sealantmaterial whereby under pressure said (deformable) flowable material is(compressed) pressed between (the) said primary and secondary pistonsand urged against the container wall to form a seal.
 2. A dispenser asclaimed in claim 1, in which the primary piston is in frictionalengagement with the wall and the secondary piston is in loose fit thusto encourage pressing of the interposed flowable sealant material.
 3. Adispenser as claimed in claim 1, in which the dispenser additionallyincludes a membranous partition wall within the propellant chamber andforming therein a propellant compartment adjacent the container base. 4.A dispenser as claimed in claim 1, in which the flowable sealantmaterial is an aqueous gel.
 5. A dispenser as claimed in claim 1, inwhich the flowable sealant material is an aqueous alginic gel.
 6. Adispenser as claimed in claim 1, in which the flowable sealant materialis gelatin.
 7. A dispenser as claimed in claim 1, in which the flowablesealant material is a viscous organic oil.
 8. A dispenser as claimed inclaim 1, in which the flowable sealant material is mineral oil.
 9. Adispenser as claimed in claim 1, in which the flowable sealant materialis an organic grease.
 10. A dispenser as claimed in claim 1, wherein theflowable sealant material is an organic liquid taken from the groupconsisting of ethylene glycol, diethylene glycol, and glycerol.
 11. Adispenser for dispensing a product under pressure of a propellantincluding a container, a composite piston system slidable in thecontainer and dividing same into a product chamber for product to bedispensed and a propellant chamber, a deformable sealant materialengaging the container wall and slidable with the piston, closure meansfor retaining propellant within the propellant chamber and a productoutlet extending from the product chamber in which the composite pistonsystem comprises a primary piston in frictional engagement with the walland having a wall-engaging skirt, a loose-fitting secondary pistonhaving a wall-engaging skirt and between said pistons a deformablesealant material whereby under pressure said deformable material ispressed between the pistons and urged against the container wall to forma seal.